The present invention relates to dot printers for reproducing halftone images, and in particular to a dot printer which overcomes the failure in reproducing halftone values below the threshold of a recording head.
Conventional recording heads employed in dot printers or the like have a threshold level below which they are not operable to produce a dot. The lack of such halftone values is detrimental to the faithful reproduction of the original.
In a prior art attempt a picture element is represented by dots of varying numbers depending on the amplitude of gray scale input to operate the recording head in a range above the threshold level. Another prior attempt involves inhibiting the recording head periodically when an input signal is below its threshold so that the average value of the optical densities of the reproduced image over a certain number of dots approximates the average value of the original densities over the corresponding period.
However, the prior art attempts have not met with wide reception because the picture quality falls short of the ideal.